This proposal focuses on the study of the second arginase gene (AII), found in eucaryotes from amphibians to man, with the goal of understanding its role in arginine homeostasis, its regulation and ultimately in exploiting it as a means of replacing deficient liver arginase (AI) activity in patients with hyperargininemia and progressive neurological and intellectual deterioration. The cDNA and specific antibodies to AII will be used to study AII regulation in prostate kidney, lactating mammary gland and macrophages, organs and cell types in which AII expression is particularly high. Special efforts will be made to define specific cell types and physiological circumstances in which AII is prominent, such a macrophage activation or prostate maturation with puberty. The relationship between AII, nitric oxide synthetase and arginine decarboxylase, enzymes sharing arginine as a substrate, will be studied as well. The mouse AII cDNA clone will be used to clone and characterize the gene in 129Sv mice. This knowledge will be used to create an AII-deficient knockout animal to define its phenotype, to define the functions of the gene product, to understand the impact of its knockout on arginine homeostasis and to define its impact on the expression of AI and other arginases (if they exist). Ultimately various combinations of deficient AI & AII genes developed from crosses of AI and AII partially or wholly deficient animals will provide the raw material to conceptualize a series of strategies, from gene activation to gene therapy, for the treatment of AI (and ultimately AII) deficiencies.